Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with cooking spray.
In a large pot, bring water to a boil. Add the cauliflower and broccoli florets and cook for 3-4 minutes until slightly tender. Drain and set aside.
In a mixing bowl, combine the softened cream cheese, sour cream, milk, garlic powder, onion powder, salt, and black pepper. Mix until smooth and well combined.
Stir in the cooked cauliflower and broccoli, crumbled bacon, and half of the shredded cheddar cheese. Mix until the vegetables are evenly coated.
Pour the mixture into the prepared baking dish and spread it out evenly. Top with the remaining cheddar cheese and panko breadcrumbs, if using.
Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the top is golden brown.
Remove from the oven and let it cool for a few minutes before serving. Garnish with chopped green onions.